When I imported some youtube feeds from an opml file they have the url like so:
https://www.youtube.com/feeds/videos.xml?channel_id=XXXXX

However, I currently have the seem feed in my rss that's:
http://www.youtube.com/feeds/videos.xml?channel_id=XXXXX

The problem is only the http one has a YT favicon. The https one ends up with a generic rss thumbnail. Since the http one redirects to https they should both have the same thumbnail.